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Here is a draft of our paper Real-time Interactive Gravitational Lensing summarizing the project. an experimental .gif animation at the bottom of this page.

At Supercomputing 98 at Orlando, Florida, November 1998

don't miss

Superball .... a.k.a. voodoo

by John Estabrook, Ulises Cervantes-Pimentel, George Francis

Voodoo is a real-time interactive computer animation for three players to inhabit the same virtual environment, two on the DuoDesk and the third in the CAVE. We use Dave Pape's "zaphod" version of the CAVE library for the 2 head tracked, 2 hand tracked Immersadesk to be installed in Orlando, and the standard CAVE library in the CAVE in Urbana. The two SGI Onyx's (shared memory parallel super-computers) driving the virtual environments talk over standard UDP protocol by means of Caterpillar's "Virtual Prototyping File Format" (VPS) libraries, courtesy Volodymyr Krindratenko and Lance Arsenault.

Since we expect serious latency problems, including total dropout of communication, the two instances, voodoo.cave and voodoo.duo, operate independently. Trajectories of some movables (the gravitational lens, the paint-balls launched by the player's avatars, etc) are locally anticipated but periodically corrected as data arrives from the distant partners. The three avatars visible in the scene, however, are kept current by VPS.

The immovable scene consists of Stuart Levy's stars at "infinity", three walls of the CAVE (the backwall features highbrow texturemapped paintings, the side wall remains a wireframe, the floor is paved with $100 bills), and a barber pole. The movables consist of the invisible "gravitional lens", the avatars and their paint-balls. We use Birgit Bluemer and John Estabrook's generalization of the classic Einstein approximation to his relativistic field equations. The lens distorts the background and also produces a second, socalled "inner image", as specified by Einstein's relativistic optics. The lens drifts about an invisible cube, bouncing off the walls.

Each player can experience Einstein's distortion, or, she can observe how this illusion is confected by cycling through the "ecstasy modes". In ecstasy (standing outside one-self) a player sees the per-vertex deformation of the scenery induced by the instantaneous location of the lens relative to another observer .

The avatar mimics its player's head and hand, and was designed by artist Kris Moskwa. Hand gestures control the motion of the player in the scene. The player can also launch a paint-ball, which drifts (more-or-less predictably) towards the intended movable target (another avatar or the presumptive location of the lens when they collide). If contact is made a signal is displayed (someday we'll use vss to make appropriate sounds) and the paint-ball returns to the avatar's wrist, marking the pivot point of the hand.

The actual performances of Superball are in the CAVE next week at these times:
Tuesday 10nov98 11am EST 10am CST,
Wednesday 11nov98 2:45 EST 1:45pm CST, and
Thursday 12nov98 11am EST 10am CST.

The actual performance of this piece is excrutiatingly sensitive to the performance of the multiprocessor onyxes and especially to the network. We have made every effort to finagle the action so that every malfunction can be blamed on others.

More pix and info, and some trophy photos from Supercomputing'98.

Here is an interim summaryof our project November 1998.